Conventionally, the navigation apparatus used in a vehicle utilizes map data retrieved from a storage unit and a current position of the vehicle derived from GPS unit for displaying the current position on a map on a display unit and for guiding a driver of the vehicle toward a destination together with other assistance.
The navigation apparatus retrieves the map data, by using a reader device such as a CD-ROM drive, a DVD-ROM drive or the like, from a storage medium of CD disks, DVD disks or the like. Alternatively, the map data may be stored in a hard disk drive (HDD).
The map data to be used for route guidance or other function is required to be updated in order to catch up the recent change of the map. The map data may be updated by just replacing the storage medium (e.g., CD-ROM) with the one having the latest data. That is, the map data update is complete when the data storage medium is replaced.
On the other hand, the map data stored on the HDD is required to be replaced with new data. Japanese Patent Document JP-A-H11-95657 discloses the map data update method of that kind.
However, the update of the map data stored on the HDD may take time due to the data volume of the map data or the like. That is, the map data used in the navigation apparatus includes various data types such as road network data for representing connection conditions of the roads, map matching data for the accuracy of positioning, facility data for representing facility information, voice data for providing voice guidance and the like.
Further, during the update of the map data, the operation of the navigation apparatus may be restricted or stopped. For example, if the old map data is completely deleted from a map data storage area for creating vacancy that accommodates the new map data, the map data can not be utilized until the completion of the storage of the new map data.
On the other hand, if the old map data is left in the storage until the completion of the storage of the new map data and the deletion of the old map data take place after the completion of the storage of the new map data, that is, if the old map data and the new map data are made to be co-existing on the same HDD, the map data storage area needs to have a greater capacity for storing both of the new and old map data.